1. Field of the Invention
The present invention relates to lubricating oils comprising base stock and containing antioxidants and dispersants.
2. Related Art
Lubricating oils, be they engine oils, or power transmission fluids (e.g., manual or automatic transmission fluids, differential oils, gear oils, etc.) must meet numerous performance goals. Not only must they effectively carry off heat but they must also protect the machinery in which they are used from friction and wear. Similarly they must be compatible with the various materials used in the manufacture of the equipment/machinery in which they are employed. Finally they must themselves be robust in resisting degradation/breakdown and must not themselves contribute to or be the cause of operating problems over the course of their use.
To achieve these sometimes contradictory goals lubricating oil compositions are made up of one or more natural and/or synthetic base stocks, and one or more of a wide variety of additives.
GB 2 384 245 for instance teaches a turbine oil composition exhibiting enhanced antioxidancy and thermal stability comprising an aliphatic ester base oil and containing aryl antioxidants. Aryl antioxidants are commonly hydrocarbyl substituted diphenyl amines and/or phenyl-alpha-naphthyl amines as well as oligomeric antioxidants formed by the reaction of diphenyl amines and phenyl-alpha naphthyl amines.
U.S. Pat. No. 6,884,761 teaches a high temperature stable lubricant mixed polyol ester composition. The composition in addition to the polyol ester compounds may also contain antioxidants such as aryl amines, i.e., dialkyl diphenyl amines, phenyl-alpha naphthyl amines, or hindered phenols, phenothiazines and their derivatives. The composition may also contain antiwear/extreme pressure additives, corrosion inhibitors, foam control additives, anti-deposition and anti-oxidative additive such as sulfur containing carboxylic acids. Hydrolytic stabilizers, pour point depressants, viscosity and viscosity index improvers, etc., can also be present. Similarly, a premixed concentrate of additives can be used such as a premix of ashless dispersants and metal detergents.
U.S. Pat. No. 4,938,880 teaches a process for preparing stable oleogenous compositions wherein high molecular weight ashless dispersants and metal detergents are preblended at a temperature of at least 100° C. for from 1 to 10 hours, cooled to at least 85° C. and combined with additional additives. Ashless dispersants comprise nitrogen or ester containing dispersants selected from the group consisting of oil soluble salts, amides, imides, oxazoline, esters or mixtures thereof of long chain hydrocarbon substituted mono and dicarboxylic acids or their anhydrides as well as the borated derivatives thereof. Other additives that can be present include copper antioxidants compounds, viscosity modifiers, corrosion inhibitors, friction modifiers, other dispersants and detergents, antifoam agents, antiwear additives, pour point depressants, rust inhibitors and the like.
U.S. Published Application 2004/0129603 teaches base stocks and base oils that exhibit an unexpected combination of high viscosity index and a ratio of measured-to theoretical high shear/low temperature viscosity at −30° C. or lower of 1.2 or lower. Such base oil can be additized with various additives individually or as an additive package. Additives include viscosity modifiers, viscosity index improvers, metallic and ashless oxidation inhibitors, metallic and ashless dispersants, metallic and ashless detergents, corrosion and rust inhibitors, metal deactivators, anti-wear agents, extreme pressure additives, anti-seizure agents, pour point depressants, wax modifiers, seal compatibility agents, friction modifiers, lubricity agents, antistaining agents, chromophoric agents, anti-foamants, demulsifiers, etc. In discussing antioxidants, several of the typical ones are identified including the hindered phenols and aromatic amines. Mixtures of two or more aromatic amines can be used as well as polymeric amine antioxidants. Dispersants include the ashless dispersants which embrace borated metal free dispersant, while dispersants in general include, e.g., hydrocarbyl-substituted succinic acid or anhydride compounds including succinimides. Boration can range from 0.1 to about 5 moles of boron per mole of dispersant.
U.S. Pat. No. 6,869,917 teaches fully formulated lubricants comprising particularly described polyalphaolefins and additives, the additives including generally the same list as presented in U.S. Published Application 2004/0129603, the antioxidant including hindered phenols and aromatic amines or polymeric amine antioxidants and the dispersant including succinimides and highly borated dispersants, the dispersants being borated with from about 0.1 to about 5 moles of boron per mole of dispersant reaction product, including those derived from mono-succinimides, bis-succinimides and mixtures thereof.
U.S. Pat. No. 6,339,051 teaches diesel engine cylinder oils of improved cleanliness and load carrying ability and reduced port deposit characteristics comprising Group I or Group II base oil, oil miscible polyisobutylene and an additive package comprising detergent, antioxidant, antiwear agent and a dispersant. The dispersant includes succinimides which may be borated or non-borated. Antioxidants include phenolic and aminic antioxidants; mixtures of two or more aminic antioxidants or polymeric amine antioxidants can also be used.
U.S. Pat. No. 5,366,648 teaches functional fluids which can be used over a wide temperature range and at very high temperature comprising at least one synthetic base oil and a minor amount of at least one phenolic compound selected from a particularly recited list and at least one non-phenolic antioxidant. Non-phenolic antioxidants include alkylated and non-alkylated aromatic amines and mixtures thereof, such asR3R4R5Nwherein R3 is an aliphatic, aromatic or substituted aromatic group, R4 is an aromatic or substituted aromatic group, R5 is H, alkyl, aryl or —R6S(O)xR7 wherein R6 is alkylene, alkenylene, or aralkylene group or mixture thereof, R7 is is a higher alkyl group or an alkenyl, aryl or alkylaryl group or mixture thereof, and x is 0, 1 or 2. R3 may contain 1 to about 20 carbons, preferably 6 to 12 carbons. Preferably both R3 and R4 are aromatic or substituted aromatic groups, and the aromatic group may be a fused ring aromatic group such as naphthyl. Aromatic groups R3 and R4 may be joined together with other groups such as sulfur.
The formulations can contain ashless dispersants which are described as dispersants which contain no metal but which can be borated. Dispersants include acylated amine dispersants or carboxylic imide dispersants such as succinimides.
Despite this extensive teaching of lubricating oil formulations containing one or more additive, it would be useful if a way could be found which still further improves the seal integrity, oxidation resistance and thermal breakdown deposit protection of a lubricating oil than has heretofore been achieved but without resort to new or exotic additives.